chlorine, sodium hydroxide, or lye, and sodium carbonate are all made from sodium chloride. and salt is needed by most living things. cows seek salt instinctively. whole herds can be moved by simply moving the salt lick. in mammals, salts are practically all dissolved into solutions of ions in bodily fluids. the concentration of the proper ions must be maintained because that concentration actually affects the cell membranes. other common salts are calcium chloride, which is spread on streets to melt ice... and stannous flouride, the salt of tin and fluorine used in toothpaste. these different salts might have different crystalline structures. the ion ratios and sizes may be different. this is a calcite crystal. the edges come together at an angle. they're not perfectly squared off like in the salt or in the halite. this is a property of calcium carbonate. the calcium ions and the carbonate ions stack together and repeat in three dimensions millions of times to build up a crystal. because of the different shape and charges of the carbonate molecules and the calcium ions, the